Jiffy is used in different applications for various short, very short, or extremely short periods of time. In informal speech a "jiffy" means any unspecified short period of time, as in "I'll be back in a jiffy", but in other contexts it has more precise definitions. The word was originally thieves' cant for lightning. The earliest technical usage for jiffy was defined by Gilbert Newton Lewis (1875-1946). He proposed a unit of time called the "jiffy" which was equal to the time it takes light to travel one centimeter. It has since been redefined for different measurements depending on the field of study.(Wikipedia)